This invention relates to a projection exposure apparatus for use in the manufacture of semiconductor circuit devices and, more particularly, to a projection exposure apparatus using an excimer laser as an illumination source for manufacturing semiconductor circuit devices.
In projection exposure apparatuses for use in the manufacture of semiconductor integrated circuit devices such as ICs, LSIs, etc., a projection system such as a lens for exposing a silicon wafer to a pattern for the manufacture of the integrated circuit must have a very high resolving power.
It is known that the resolution in the image projection by the projection lens can generally be improved with the use of a shorter wavelength. For this reason, illumination sources emitting shorter wavelengths are usually employed. For example, a wavelength of 436 nm or 365 nm by an Hg lamp is currently used in most projection exposure apparatuses.
Excimer lasers (excited dimer lasers) providing short wavelengths are known. The excimer lasers use, as their lasing media, gases of ArF, KrCl, KrF, XeBr, XeCl, XeF, etc. According to the lasing medium used, the excimer laser produces light of a single wavelength, or a very narrow wavelength range within the region of 150 nm-400 nm, which is pulseoscillated at a repetition frequency of 200-300 Hz.
Application of the excimer laser to the photolithography is described in "Study on Laser" vol. 8, No. 6, November 1980, pp. 69-71 ("PhotoEtching of PMMA by Excimer Laser"), published by Japanese Laser Society.